1. Field of the Invention
The present invention relates to a cutting spindle unit for a cutting machine, especially a router for wood working and, in particular, to a double cutting spindle unit comprising a main spindle unit and a sub-spindle unit mounted on the main spindle unit and being vertically slidable relative to the main spindle unit.
2. Description of Background Art
In recent years, it has been proposed to provide a router for wood working having a double cutting spindle unit comprising several main spindle units each being mounted slidably vertically on a planer-type frame, and a sub-spindle unit also mounted slidably vertically on each main spindle unit, with the main and sub-spindle units being able to integrally move along the Y-axis direction as well as being able to separately move along their axial (i.e., Z-axis) directions in order to increase the number of places to be simultaneously cut by the router and also to reduce the frequency of tool exchange.
The mounting of tools to the spindle units are carried out by the collet chuck mechanisms both in the main and sub-spindle units. However, there is a difference between the sub-spindle unit and the main spindle unit in that the collet chuck of the sub-spindle unit is manually actuated, whereas the main spindle unit is remote-controlled by a powered actuator.
The powered actuation of the main spindle unit will be hereinafter described with reference to FIG. 4. An end of a spindle 22 of the main spindle unit 20 is formed with a tapered bore Aa, and a collet chuck Ab is positioned inwardly adjacent to the tapered bore Aa. After having inserted a tool attachment Ba into the tapered bore Aa, the collet chuck Ab is fastened by the force of belleville springs Ac and thus the tapered portion of the tool attachment Ba is pulled into the tapered bore Aa and frictionally engages the inner surface thereof. In order to remove the tool attachment Ba from the spindle 22, a piston rod Cb is projected by a pneumatic cylinder Ca having a large diameter. The power of the piston rod Cb is boosted by a lever Cc and pushes an actuating shaft 26 downward against the force of the belleville springs Ac to release the collet chuck Ab. Simultaneously, the front end 26a of the actuating shaft 26 abuts the rear end of the tool attachment Ba to release its frictional engagement with the tapered bore Aa. A reference character "Cd" denotes a stopper for the lever Cc. In general, wood working machines which generate sawdust or woodchips typically use pneumatic cylinders as hydraulic actuators, which can experience oil leakage problems.
Since the size of the sub-spindle unit is required to be small, the outer diameter of the collet chuck should be small and its detachable mechanism should be simplified. In addition, the opening and closing operations of the collet chuck and the pushing-out operation of the tool attachment are carried out by a manually operated screw shaft (not shown). Since such a manual operation requires substantial time and labor for mounting and demounting of the tool attachment, it is desired to develop a collet chuck which can be operated by power and also can fulfill the requirements of small size and light weight.
However, there are several problems which must be overcome before the successful development of such a collet chuck can be realized. Firstly, it is impossible to get a small and powerful power source used for mounting and demounting the tool attachment to and from the spindle. As previously mentioned, the mounting of the tool attachment Ba to the collet chuck Ab of the main spindle unit is carried out by the force of a plurality of strong belleville springs Ac and the demounting of the tool attachment Ba therefrom is carried out by the pneumatic cylinder Ca. However, such a mounting and demounting mechanism of the main spindle unit cannot be applied to that of the sub-spindle unit due to potential interference of the sub-spindle unit with the main spindle unit if the outer diameter of the sub-spindle unit is increased to accommodate a large diameter power cylinder or a boosting lever which can generate sufficient power to overcome the force of the belleville springs.
Secondly, there is practical difficulty due to instability of the spring constant of the belleville springs caused by the mutual friction between springs when using belleville springs of small diameter to be accommodated within the sub-spindle casing.
Thirdly, there is the problem of preventing the mutual interference between the main and sub-spindle units during tool exchange of these spindle units. That is, in the case of the sub-spindle unit of the prior art which is manually operated to mount or demount the tool attachment, the lower stroke limit of the sub-spindle unit is set at a position higher than that of the main spindle unit in order to prevent the interference of the sub-spindle unit with the main spindle unit since the tool of the manually operated spindle unit is not required to be lowered to the position of the automatic tool exchanger of the main spindle unit. Moreover, with a sub-spindle unit that is automatically operated to mount or demount the tool attachment, if the tool attachment is lowered to the position of the automatic tool exchanger, there would be caused an occasion in which the presence of the tool attachment of the sub-spindle unit will interfere with the tool exchange of the main spindle unit or an occasion in which the presence of the main spindle unit will interfere with the exchange of the tool exchange of the sub-spindle unit.